How to Land Robots on the Moon (and Keep them Alive)

Getting robots to the moon and keeping them running in the atmosphere-free, cold and dusty environment presents one of the biggest challenge lunar-rover researchers have ever faced. Last week the U.S. Chamber of Commerce hosted a NASA workshop about the hardware that could make the moon a home. Here is one plan on how rovers might be kept functional on the moon despite the harsh conditions.

As the space community eagerly awaits the nomination of the next chief administrator of NASA, and maybe a new direction in human exploration programs, the agency's plan to revisit the moon continues unabated. The Lunar Reconnaissance Orbiter (LRO), a satellite that will map the moon in unprecedented detail, is expected to launch in late May--providing data to help NASA plan an outpost location for an extended stay.

After the LRO is launched but before astronauts arrive, rovers are likely to do the heavy lifting--as scientific researchers and construction workers--to get the outpost up and running. Getting them there is easier said than done. Landing payloads on Mars--which is about 500 times farther away than the moon--is easier to accomplish because the planet has an atmosphere that slows down incoming landers. Without the natural brakes that an atmosphere provides, a crippling crash onto the surface is very possible. Once a rover has touched down on the Moon, conditions on the surface--with severe temperature swings and gritty soil--are likely to play havoc with machinery and sensors.

For humans return to the moon, engineers are now focused on innovations in hardware, including power systems, habitation designs, specialized tools and software. Such innovation was the central focus of a NASA workshop last week hosted by the U.S. Chamber of Commerce. Presenters made public their research into novel power systems, new designs of habitation modules, unique software and enabling technologies that might be used to establish a lunar base. (PDFs and animations of the presentations are available here).

While some researchers, such as Astrobiotic Technology and Carnegie Mellon, focused on the hardware needed for humans--like a study that explored how a 300-pound robot can create a landing pad out of a combination of melting and bulldozing regolith--others focused on how to keep the robots alive in the extreme cold of the lunar night.

Near constant sunlight makes the moon's south pole an ideal spot for a base. When in direct sunlight, surface temperatures can reach 280 F. But the sun is always low in the sky, and the chilling shadows cast by mountains are long. The moon's slightly tilted axis and the deep shadows caused by the terrain can drop temperatures to less than -200 F.

"Robotic systems will have difficulty surviving this extreme cold," says Robert Wegeng, chief engineer at Pacific Northwest National Laboratory's energy and efficiency division. At the workshop, Wegeng, in collaboration with NASA's Kurt Sacksteder and Nantel Suzuki, devised a new way to keep the pioneering robots warm, with slabs of melted lunar soil to store heat in what they call "thermal wadis." If you keep the 'bots over around -63 F, they'll still function--the researchers calculate the wadis can keep rovers at -15 F.

The reason melted moon rock stores heat has to do with lunar history--the surface material is a coarse dust created by rocks that were pulverized by meteorites. The result is sharp-edged dust particles that readily conduct heat. "You have to melt the regolith and then resolidify it into a rock- or glass-like form that can store heat," Wegeng says.

This melting can be done in a number of ways, including directly fusing it with a large lens, removing oxygen via a chemical reaction, utilizing microwave energy to make thermal bricks or using electrodes to zap the regolith so that the soil's resistance to the current produces heat.

Heat could be retained within these thermal pads of resolidified soil by using umbrellas-like reflectors. (The umbrellas would configure themselves while in the sun to redirect light to the thermal pads.) A network of these heated oases could provide rovers warm places to roost during periods of lunar darkness. "I sometimes think of these rovers huddled under Starbucks umbrellas, having lattes on top of the thermal mass, while they wait for the lunar darkness to end," Wegeng says.

After an outpost is established--NASA is shooting for 2020--a network of thermal wadis might remain useful for robots used for long-duration surveys and other scientific research on the surface, Wegeng says, including extending the range of human-occupied rovers.